The drilling of an oil well usually employs so-called "mud" which is a weighted liquid that is pumped down through the drill string and out the nozzles of the drill bit, where it circulates up through the annulus between the drill string and the wall of the borehole and returns to the surface. Here the mud is processed to remove cuttings and then fed to a pit where it is available for additional circulation down the drill string. The mud performs several vital functions in connection with the drilling of a well, for example it cools the bit, carries rock cutting from the bit to the surface, and prevents a blow out by overbalancing the pressure of fluids in the earth formations penetrated by the borehole. The various density-increasing additives which are used to form the drilling mud also tend to filter into the formation and thereby form a mud-cake on the hole walls which stabilize it. The increased thickness or mud-cake that is formed provides an indication of those formations which are more permeable than others.
When the drill pipe string is being removed from the well, for example to substitute a new for a worn bit, the drilling mud that remains in the string can cause serious problems. Typically the derrick of the rig is tall enough that the drilling string can be removed and stacked in "triples", that is to say only every third connection is unthreaded so that a series of three pipe joints still connected together (stand) are stacked in the derrick for later re-running. However approximately a 90 ft. column of drilling mud remains inside each stand as it arrives at the surface, so that when a threaded joint is disconnected, the mud suddenly spills onto the rig floor where a portion of it goes through and onto the ground or water surface therebelow, while other portions splash onto rig personnel and onto various parts of the rig around the floor. Not only is a very messy and hazardous situation created each time a joint is disconnected, which requires a thorough clean up, the total volume of spilled and wasted mud can have serious impact in the economics of drilling, not to mention ground or water pollution which can have a serious ecological impact.
In an attempt to prevent spillage, one device that has been used is shown in the 1978-79 "Composite Catalog of Oilfield Equipment and Services", Vol. 3, page 5303. This device comprises a barrel assembly having hinged halves which carry diametrical split seals at its upper and lower ends that engage outer peripheral surfaces of the drill pipe. After a threaded pipe connection has been spun loose, but not yet actually separated, the assembly is positioned and latched closed around the pipe. Then when the stand of pipe is raised upward, the mud therein is dumped into the barrel where it is carried away by a swivel mounted drain line. However repeated upward movements of the drill pipe through the split seal at the upper end of the barrel soon causes considerable wear on the upper seal due to the rough and abrasive nature of the outer pipe surface. Soon the upper seal begins to leak mud out on the rig floor so that expensive drilling muds are lost and the rig floor must be washed down or else accidents will occur due to slippery conditions.
Another device that has been offered is a so-called "mud bucket" which is designed for use with a drilling rig having an automatic pipe handling system, and is opened and closed by hydraulic cylinders which are mounted on a massive scissor-like structure that enables remote control. This device is extremely expensive to make and to maintain, and is subject to failure in the event the hydraulic lines leak or are disrupted by pipe handling operations in the derrick or on the rig floor.
An object of the present invention is to provide a new and improved means to contain and save the drilling mud which comes out of the lower end of a length of a drill pipe when a threaded joint at its lower end is disconnected.
Another object of the present invention is to provide a new and improved tubular container assembly that is removably positioned around a drill string adjacent a threaded connection therein to catch and save the mud coming out of the lower end of the upper threaded joint as the connection is replaced.